This invention relates to a method and apparatus for increasing the average coefficient of performance of a multiple-stage refrigeration or cooling system.
In the past, the cycling of stages of a multiple-stage refrigeration or cooling system has been principally accomplished by setting each stage at a successively lower "cut-in" and "cut-out" pressure of the refrigerating fluid flowing in the suction line from the evaporator coil to the compressor(s) or cooling stages. The use of successively lower "cut-in" and "cut-out" pressure ranges for each cooling stage results in an average pressure which is lower than the mean pressure of the pressure differential between the "cut-in" and "cut-out" pressures of the highest stage. Various mechanical and electromechanical systems have been devised to attempt to solve this problem, primarily utilizing the successively lower pressure ranges for each successive cooling stage as described above.
Patents which are typical of the prior art for electromechanically controlling refrigeration compressor capacity include the following U.S. Pat. Nos.: 3,885,938; 3,828,152; 3,719,057; 3,581,519; 3,580,006; 3,552,137, and 3,377,816.
Increased efficiencies in a multi-compressor refrigeration system having at least one variable speed compressor could be realized if each cooling stage could be controlled at a single highest "cut-in" and "cut-out" pressure levels that would ensure adequate temperatures in the refrigerated space served by the evaporator coils, and by enabling the compressors to energize and deenergize when the variable speed compressors have attained their respective maximum and minimum speeds.